Pressure actuated valve



y May 22, 1945- D. G. TAYLOR l PRESSURE ACTUATED VALVE Filed Aug. 11,1941 suvmy TO VALVE BACK PRESSURE.

Af ion/Lew Patented May 22, 1945 PRESSURE Ac'rUATEn VALVE Daniel G.Taylor, Minneapolis, Minn., assigner to r Minneapolis-HoneywellRegulator Company, Minneapolis, Minn., a corporation of DelawareApplication August 11, 1941, Serial No. 406,351

V18 Claims. (Cl. 236-10) The present invention is directed broadly tovalves which are operated by means of a pressure actuated motor, and ismore particularly concerned with a pressure actuated valve in which' thepressure in the actuating motor is controlled by a pilot valve assemblycontrolled jointly by a condition responsive device and a follow uparrangement whereby the main valve may be modulated in accordance withthe' value of the condition to which said condition responsive deviceresponds.

In many valves of this type, particularly where they control the ow ofgas to a burner, itlis desirable to modulate the valve between a fullopen andminimum open position land to operate the valve rapidly betweenminimum open and closed positions.

It is therefore one of the main objects of thisl invention to provide avalveof the modulating type described above, with mechanism foroperating it. rapidly between closed and minimum l open positions.Another object of the invention is to make this mechanism in the form ofla snap action device which operates on the pilot valve assembly, andwhich is normally inactive but which is rendered active when the mainvalve reaches a minimum open position.

Another object is to provide a valve of the follow up type, as describedabove, with4 a means for limiting the maximum pressure at the outlet ofthe main yregulating valve.

A still further object is to adapt a valve of the above type to thevcontrol of thc flow of gas toI novel valve actuating mechanism.

Referring now to Fig. l, the reference numeral I0 indicates aconventional hot air furnace which is heated by the usualform of gasburner II. Gas is fed from a source of supply, not shown, through asupply pipe I2 to a diaphragm gas valve indicated generally at I3. Thevalve I3 controls the ilow of gas in the supply pipe I2 y through thepipe I4 yto the gas burner II. The

bypass pipe I5 connects the pilot burner I6 for the main burner IIdirectly, with the supply pipe I2. t

The diaphragm gas valve I3 is of the conventional type which is providedwith a diaphragm member I8 for controlling the position of the valve I9which in turn cooperates withthe valve seat 26 to controlthe flow of gasfrom the supply pipe I2 to pipe I4. A cover 22 peripherally clamps the`diaphragm I8 against the valve body 23 to form a pressure chamber 24above the diaphragm. The position of the valve is dependent upon thepressure in the pressure chamber 24. When the pressure in this chamber'is equal to` the pressure in the supply pipe I2, then the pressures onopposite sides of thediaphragm are equal and the diaphragm moves thevalve to closed position by gravity. When the pressure chamber 24 isvented to the atmosphere the supply line pressure beneath the diaphragmI 8 is effective to raise the diaphragm and move the valve to wide openposition. For all pressures between these two limit pressures. the valvewill have a corresponding position between fully opened and fully closedpositions so that'the rate of flow of gas past the valve may beregulated by regulating the pressure in the pressure chamber 24.' l

The reference numeral 25 indicates a casing which houses the operatingmechanism for'the pilot valve assembly indicated generally at 26 inFigure 2 which controls the pressure in the pressure in the pressurechamber 24. The pipe 21 show-n in Fig.' 1 connects the supply pipe I2directly with the valve chamber 28 shown in Fig. 2.

, The pipe 29 shown in Fig. 1 connects the pres-v sure chamber 24directly with the control chamber 30 shown in Fig. 2, and the pipe 31shown in Fig. 1 connects valve chamber 32 shown in Fig. 2 directly withthe atmosphere. For the sake of convenience, the pipe 3l terminatesadjacent the gas burner Il so that the gas bled through this pipe may beconsumed.

The control chamber 30 shown in Fig.v2 is sealed from the atmosphere bymeans of the diaphragm 35. Supply valve 36 controls the ilow of gas fromthe supply chamber 28 to the control chamber 36, and the exhaust valve31 controls the flow of gas from the control chamber 30 to theatmosphere through pipe 3l. Valves 36 and 31 are controlled respectivelyby means of screws 39 and 40T which are adjustably positioned` in lever4I which is .pivotally mounted on the pilot valve assembly as shown at42. With the lever in its horizontal position as shown in Fig. 2, bothof the valves 36 and 31 are closed and therefore the pressure in thecontrol chamber 80 and hence the pressure chamber 24 remains clockwise,the supply valve 88 is opened to increase the pressure in the pressurechamber 24 and hence move the valve I8 toward closed position. s Thereturn of lever 4Ij to horizontal positio'n stops the increase inpressure in the chamber 24'and the valve I8 will then remain stationary.

A clockwise rotation of lever 4I will open thel exhaust valve 81l andpermit the leakage of gas from chamber 24 to the atmosphere, hencecausment of valve I8 will result in an increase in the outlet pressurein pipe I4 which will result in the constant. When the lever 4I isrotated countering a decrease in pressure in chamber 24 and Aconsequently a movement of the valve I8 toward openposition. It willtherefore be seen that by properly controlling the lever 4I, thepressure in the kchamber 24 and hence the position of the valve I9 maybe accurately controlled.

The rotationof the lever 4I is controlled by means of lever 45 which ispivotally mounted 'as shown at 48, to the bracket 41. Lever 45 isconnected to lever 4I by means of pin 48 which is slidably receivedbetween the two legs 48 oi' the bifurcated end of the lever 1I. Rotationof the lever 45 will therefore cause a corresponding rotation of thelever 4 I.

The lever 45 pivotally carries a second lever 58 'as shown at 5I. Theright end or the lever 50 is .provided with an upstanding portion 58which adjustably carries a nut 54 by means of screw 55. One end o1' thetension spring 55 is connected to the nut V54 and the other end islooped into an ear 51 on lever 45. The function of the tension spring58l is to tend to produce relative rotation between the two levers 45and 58 which follow-up diaphragm 84 exerting an increased upward forceon lever 50 which will return the lever 4I to horizontal position asshown in Fig. 2. Conversely, if the downward force exerted by lever 68on lever45 is reduced, the lever 4I will be rotated in a direction toopen the supply valve 88 causing an increase in the pressure in thepressure chamber 24 and a movement of the valve I8 toward closedposition by the diaphragm I8. The resultant reduction in outlet pressurewill cause the follow-up diaphragm 64 to reduce its eilect on lever 50and the lever 4I will again return to horizontal position in which boththe supply and exhaust valves 35 and 81 are closed. Thus it will be seenthat a change in the pressure exerted by lever 58 or lever 45 willresult in a movement ,of the valve I8 and that the resultant change inoutlet pressure in pipe I4 will profduce a follow-up action by thediaphragm 84 to would tend to separate their two ends58 and 58.

The screw 55 has a screw-threaded engagement with the nut 54 so thatrotation of screw 55 will f produce a longitudinal movement of the nut54 with respect to the spring 58, extension 80 on the nut 54 preventingrotation thereof due to the fact that it is slidably received in a slotin the portion 53 of the lever 50. Rotation of the screw 55 thereforeadjusts the .tension of the tension spring 58. v A

The cup-shaped member 58 circumferentially clamps a pressure responsivediaphragni 84 to the casing 25, thereby forming a pressure chamber 85which is connected by means of pipe 88 shown in Fig. l with pipe I4which is on the outlet side of the valve I8. The pressure in the chamber85 is therefore equal to the outlet pressure of the valve I9, andvariations in this pressure are communicated to the lever 50 by means ofthe rigid connection 58.

The lever is connected by a pin and slot connection shown at 81 -to anactuating lever indicated generally at 88. During normal operation, thelever 88 will exert a force on the lever 45 tending to rotate itdownwardly and at the same time the effect of the outlet pressure on thediaphragm 84 is to rotate the lever I8 upwardly. Normally, these forcesare sumcient to overcome the force exerted by spring 58 and maintainthese levers in parallel relationship as shown in Fig. 2, at which timethe ear 58 on lever 58 will engage the lever 45. Underthese condi- Ations, the two levers 45 and 50 will'operate together as a unit tocontrol the pilot valve actuating lever 4I. Speclncally ii lever 58exerts an increased downward force on lever 45 it will ro- Fig. 2,against the rotative force exerted by the stop the movement of the valve|8. All this time the two levers v45 and 50 are moving together as aunit.

Lever 10 is pivotally carried by the lever 45 as indicated at 1I. At oneend, the lever 1I| rotatably carries a screw 12 which in turn is inscrewthreaded vengagement with the nut 13 which carries one end of atension spring 14, the other end being looped into the lever 45.Rotation of screw 12 will vary the tension of spring 14 by causing alongitudinal movement 0f nut 18 which is prevented from turning by anextension 15 which is slidably received in a slot in the end 18 of thelever 1l).- 'I'he spring 14 tends to rotate lever 10 in a clockwisedirection with respect to the lever 45 which would tend to move the end18 of lever 10 toward the left. With the two levers 45 and 50 in theposition shown in Fig. 2, the toggle link 18 which connects the end 18of lever 10 with the ear 88 on .lever 50 is parallel to the levers 45and 50' and is in direct alignment with the pivotal connection 5Ibetween levers 45 and 58. In other words, the toggle link 18 is in deadcenter position with respect to levers 45 and 58 and hence has norotative eflect on them at this time. l

As stated above, as long as the outlet pressure and the pressure exertedby the lever 58 on lever 45 are above a predetermined value, they willhold the levers 45 and 50 together, as shown in tension spring 58. Atthis time the twolevers are movable as a unit back and forth between thetwo stops 80 and 8l on the bracket 82, .as

' soon as these two forces decrease below a predetermined value, thetension spring acts to produce relative rotation between the levers 45and 50 separating their two ends 58 and 58. This moves the toggle link18 out of its dead center position at which time the spring 'ul causes astop 80, such operation occurring with a snap action. This operation ofcourse rotates the lever 4I to a position where the supply valve 35 ol'the pilot valve assembly will be wide open and the exhaust valve 31closed, at which time the valve 2,316,895 3 justed by adiustingspring 83through the screw I9 will be closed and the pressure in the chamber.65therefore reduced to atmospheric.

In order to open the vvalve |9the lever 6l must -exert a downwardforceon the `lever 45 which is sufficient to overcome vthe effect of both ofsprings 56 and 14. As the lever'45begins to rotate ina counter clockwisedirectonas a. result.

, Vwillhave been reduced tozero. At this time lever 4I willhave openedthe exhaust'valve 31 and closed supply valve 36, thus relieving thepressure in chamber 24 and permitting valve I9 to open. When the outletpressure in chamber 65 balances the downward force exerted by lever 68,diaphragm 64 will return the levers 45 and 50, as a unit, to theirhorizontal position, closing both the supply and 4 .exhaust valves 36and 31. The mechanism will now function as before to maintain an outletpressure dependent upon the downward force exerted by the lever 68.

The above described mechanism is so related that the spring 56 will beeffective to operate thetwo ends 58 and 59 of levers 45 and 50 when thepressure in chamber 24 has been increased to such'a pointthatvitpositions the valve in a open position beyond which it would beundesirable to modulate the valve. In other words, it is desirable tomove the valve uninterruptedly to closed `position from this minimumopen position Vand such action is provided for by the above describedmechanism. On opening the valve, it will be noted that thev lever 58must overcome the action of the tension spring 56 and the force exertedby spring 14 through the toggle link'19 in order to close the supplyvalve 36 and open the exhaust'valveA 31, because this can b eaccomplished only by producing relative rotation between the two levers45 and 50, lever 50 being held in engagement with the stop 80, In orderto accomplish this,j,the condition to which the vlever 68 is' responsivemust have attained a value corresponding to a certain open position forthe valve.- Whenthisf value is attained, lever 45 will be snapped intoengagement with ear 69 on lever 50, thus opening the exhaust valve 31and permittingrvalve I9 to open. The outlet pressureV in chamber 65will-increase until the diaphragm 64 balances the force exerted by lever68 at which time the two levers 45 and 50 will move as a unit as before.

f The condition responsive lever indicated generally at 68 is composedof a first lever 84 pivoted -on knife edge 85 of the-bracket 86, lever84 pivotally carrying a second-lever 81 as shown at 11. Lever 81 carriesa pin 89, the lower end of which is normally held against lever 84 bymeans of 86. One end of the lever 84 is adjustablyconnected as, shownkat 92 to a temperature respon-` sive bellows shown in dotted lines at93. This bellows communicates by capillary tube 94 with a bulb shown at95 in Fig. l as being located in the v return air duct 96 which leadsfrom the' space to be heated, not shown, back tol the furnace Ito bereheated. A main adjustment spring for the lever 84 is shown at 98 andis adjustably connected to the lever 84 as shown at 99. Theupper end ofthis spring is connected toan adjustment nut |00 which screw-threadedlyengages the ad- I Justment screw |0|. An extension |02 on the nut |00slidably engages a slotin the adjustment housing |08 to prevent itsrotation so' that rotation of `the screw IOI will vertically adjust thenut |00 and hence adjust the tension of the spring 9 8. A

A bimetallic helix |05 is inserted in the bonnet of the furnace I0shown'in Fig, l in order to tension spring 83. Spring 83 is carried atits upper end by the-nut 9| which is in turn adjustably car-ried by thescrew 88 which extends loosely throughan opening in the lever 81. 'I'hellower end of spring 83 is connected to the nut 91, a portion of whichstraddles pin 89 to prevent rotation of the spring 83 when the adjustingscrew 88 is rotated. Nut 91 is supported by screw |04.

It will be seenby the above construction that the lever transmits itsforce tolever 91 and hence to lever 45 through spring 83. Spring 83therefore limits the rotative force which can be transmitted to lever 45by lever 84 and hence limits the maximum outlet pressure. of the valveI9. This maximum outlet pressure may be adrespond to the temperature ofthe air being delivered to the space to be heated. A This helix isadapted to rotate shaft |06 oflig.` 2 which is in turn connected to anarm |01. Arm |01 is connectedn by means of a pin and slot connectionshown at |08 to an ear |09. on the lever 81. It

will be noted that the he1i-xLI05 is shown as extending from the rightside of the vcasing 25 in Fig. 1. This is done merely for the sake pfconvenience, the preferred construction. being as shown in Fig. 2 wherethe helixrextends from the rear of the casing.

From the above, it will be seen that both the bimetal helix |05 and thetemperatur'emresponsive bellows 93 affect the rotation ofthe lever 68,the resultant force exerted by this lever on the lever 45 being a.function of both the bonnet temperature and the temperature of thereturn air. Specifically, an increase in temperature of the return airwill cause a downward movement of the connection 92 as seen in Fig. 2and hence a clockwise rotation of the lever 68. Assuming that the lever4| is in horizontal position and both the supply and gas valves 35 and36 closed, this action will open the supply valve 36 -to increase thepressure in the pressure chamber 24 and hence move the valve I9 towardclosed po sition. 'I'he resultant reduction inV outlet pressure willdecrease the pressure in the chamber 65 and reduce the force exerted bythe diaphragm 64 on the lever 50. This reduction in force willccunterbalance the reduction in force exerted on lever 45 by the lever66 and hence the lever 4I will return to its horizontal position whereinboth valves 36 and 31 are closed. This follow up action by the diaphragm461| provides for a definite position Vof the valve for every forceexerted by the lever 68 on lever 45 as a result of the temperatures atthe bimetal |05 and the -thermal bulb 95 which communicates withbellows'93. An increase in the bonnet temperature will cause the helix|05 to vrotate shaft |06 in a counter-clockwise direction and thereforedecrease the force exerted by lever 68 on lever 45. This will cause vafurther closure of the valve in the same manner as vdescribed above. Adecrease in temperature at the helix |05 or bulb 95 will Acause anopposite action. that is, an increase in the force exerted by the lever68 on the lever 45 which will result in decreasing the pressure in thechamber 24 and hence increasing the outlet pressure `in chamberwhereupon thev diaphragm 64 will increase the pressure exerted on-thelever 50 to 4 aavasas balance the increased force exerted by lever 60 onlever 45.

As explained above, if the temperature should rise at the helix |05 andbulb 95, to the point where the valve I9 has been moved to a minimumopen position. then the forces exerted on the lever 45 by the lever 68and the counterbalancing or follow up force exertedon the lever 50 bythe diaphragm 64 will be so reduced that the spring 56 will be capableof separating the iends 58 and 59 of the levers 45 and 50 and the spring'Il will come into action to cause this movement to take place with asnap action. This results in supply valve 36 being opened and remainingopen to cause the valve I9 to' move directly to closed position. Thisvalve cannot be reopened until the temperature at the helix |05 and bulb95 has decreased sumciently to cause the lever 68 to exert suihcientforce on lever 45 to overcome the effect of both springs 56 and 'I4 androtate the lever 45 with a. snap action against ear 69 on lever 50 andclose supply valve 36 and open exhaust valve 31. l This reduces thepressure in the chamber 24 causing the valve I9 to open and therebyincrease the outlet pressure in chamber 65. Eventually Vthis pressurewill be` sui'cient to balance the force exerted by lever 68 at whichtime levers 45 and 50 will be returned to their |I3, upon rotation ofthe lever 84 between its two limit positions as determined by the stops||l and ||8 on bracket IIS, passes back and forth overcenter withrespect to the pivotpoint 85 of lever 04. The purpose of thisarrangement is not to produce a snap action but to introduce a forcewhich will, to a certain extent, compensate the spring rates of thebimetal |05, adjusting spring 98, and bellows 93, and therefore increasethe sensitivity of these members. If these 'members were suiiiclentlysensitive to produce the desired control, then the lever ||5 with itstoggle I|3 would be unnecessary. The upper end of the spring I6 isconnected to the nut |02 which is prevented from rotating by extension|2| slidably received in a slotin bracket |22. Adjusting screw |23screw-threadedly engages the nut |20, and upon rotation causes avertical adjustment thereof to adjust thetension of this spring.

It will thus be seen that I have 'provided a valve actuated mechanismwherein the pilot v'alve assembly or apressure operated main valve is socontrolled as to modulate the main valve between full open and minimumopen positions which will cause uninterrupted movement of the main valvee between minimum open position and closed position. Various changes andmodiiications of the above invention will doubtless occur to those whoare skilled in the art, and I therefore wish it to be understood that Iintend to be limited only by the scope of the appended claims and not bythe specific embodiment disclosed.

I claim as my invention:

1. In combination, a main valve for controlling the flow of a uid, apressure responsive motor for modulating the valve, pilot valve meanscontrolling. the pressure in said pressure motor, a movable member foractuating said pilot valve means, a device responsive to a controllingcondltionand exerting a force on said memberdepending upon the value otsaid condition, follow up means responsive to the pressure on the outletside of said main valve for balancing said torce and thereforemodulating the position of said main valve, means opposing both theforce exertedby said condition responsive device and that exerted bysaid follow up means for actuating said pilot valve means in a directionto cause closure of said main valve when the forces exerted by saidcondition responsive device and said follow up means decrease below apredetermined valve, and means for rendering said last named meanssubstantially ineiective to ai'ect tne position of said movable memberuntil said forces decrease below said predetermined value.

2. In combination, a main valve for controlling the ilow of a fluid, apressure responsive motor for modulating the valve, pilot valve meanscontrolling the pressure in said pressure motor', a movable member foractuating said pilot valve means. a device responsive to a condition andexerting a force on said member depending upon the value of saidcondition, follow up means responsive to the pressure on the outlet sideof said main valve for balancing said force and therefore modulating theposition of said main valve, and means including spring actuated snapaction mechanism for actuating said pilot valve means with a snap actionin a direction to cause closure of said main valve when the opposingforces exerted by said condition responsive device and said follow upmeans decrease below a predetermined value.

3. In combination, a main valve for controlling the flow of a uid, apressure responsive motor for modulating the valve, pilot valve meanscontrolling the pressure in said pressure motor, a condition responsivedevice, connections between said condition responsive device and saidpilot valve means whereby the latter can be actuated by the former,follow up means operating in response to pressure on the outlet side ofthe main valve and operative upon said connections, and power means insaid connections opposing both said condition responsive device and saidfollow up means with a predetermined force for operating said pilotvalve means to close said main valve when said main valve has been movedby said condition responsive device to a position where the forcesexerted by said condition responsive device and said follow up means arebelow' said predetermined force of the power means.

4. In combination, a main valve for controlling the iiow of a fluid, apressure responsive motor for modulating the valve, pilot valve meanscontrolling the pressure in said pressure motor, a first pivoted leverfor actuating said pilot valve means, a device responsive to acontrolling condition for exerting a force on said rst lever which isdependent upon the value of said condition, a second lever pivotallymounted on said ilrst lever, andfollow up means exerting a force on saidsecond lever which is dependent upon the pressure on the outlet side ofsaid main valve, and biasing means acting against both of said forcestotend to cause relative rotation of said levers, said two forcesnormally holding said two levers in predetermined relation against thebiasing means .whereby they move as a unit to actuate said pilot valvemeans and Ymodulate the position of said main valve in accordance withasvacas trolling the pressure in said pressure motor, a

nrst pivoted lever for actuating said pilot valve means, a deviceresponsive to a controlling condition for exerting a force on said ilrstlever which is dependent upon the value oi said condition, a second.lever pivotaliy mountedon said ilrst lever, follow up means exerting aforce on said second lever which is dependent upon the pressure ontheoutlet side of said main valve, biasing means acting against both ofsaid forces v to tend to cause relative rotation of said levers, saidtwo forces normally holding said two levers in predetermined relationagainst the biasing, means whereby they move as a unit to actuate saidpilot valve means and modulate the position of said main valvein'accordance with the value of said condition, said biasing means beingeiec. tive when sad forces decrease below a. predetermined value tocauseI relative rotation between said levers whereby said ilrst leveractuates said pilot valve means to cause said main valve to moveimmediately to closed position/ and snap action means inactive when saidlevers are in said predetermined position but active when said biasingmeans causes relative movement between said levers for moving saidlevers with a snap action.

6. In combination, a main valve for controlling devices tor exerting aforce on said movable member which is dependent upon the average oi thevalues of the conditions to which said two devices respond, follow upmeans responsive to the pressure on the outlet side of said main valvefor balancing said force and therefore modulating the-position ofsaid-main valve, means opposing both the force exerted by said conditionresponsive device and lthat exerted by said follow up means foractuating said pilot valve means in a direction to cause closure of saidmain valve when the forces exerted by said condition res ponsive devicesand said follow up means decrease below a predetermined value, and meansfor rendering said last named means substantially ineffective to affectthe position of said movthe flow of a iluid, a pressure responsive motorfor modulating the valve, pilot valve means controlling the pressure insaid Vpressure motor, a iirst pivoted lever for actuating said pilotvalve means, a. device responsive to a controlling conv dition forexerting a force on said ilrst lever which is dependent upon the valueof said condition, a second lever pivotallymounted on said ilrst lever,follow up means exerting a force on able member until said forcesdecrease below said predetermined value.

8. A control system for gas burners comprising i in combination, a gasburner for heating a iluid to be circulated through a space to beheated, a main valve controlling the ilow of gas to said burner, apressure motor 'for actuating said valve, pilot valve means controllingthe pressure in said motor, a movable member for operating said pilotvalve means, a first thermostat responsive to the temperature of theheated iluid. a second thermostat responsive to the temperature of theiluid returned from said space, means connected to said two thermostatsfor exerting a force on said member dependent upon the average of thevalues oi said two temperatures, and follow up means exerting a force onsaid member dependent upon the pressure on the outlet side of said mainvalve whereby said member operates saidA main valve'to modulate it in.accordance with the average of said two temperature values.

- pilot valve means controlling the pressure in said second lever whichis dependent upon the pressure on the outlet side of said main valve. anrst spring carried by said levers and acting against both forces toproduce relative rotation between said levers, said two forces normallyholding said two levers in predetermined relation against the forceexerted by said iirst sprint.r whereby said two levers move as -a unitto actuate said pilot valve-means and modulate the position of said mainvalve in accordance with the. value oi' said condition. snapaction'means including a second spring andy toggle link carried by saidlevers, said toggle link being substantially in dead center positionwhen said two levers are in said predetermined relation. said ilrstspring being eilective when said forces decrease below a predeterminedvalue to cause relative rotation between said levers thereby moving saidtoggle link out of dead center position and rendering said second springoperative to cause said levers to move with a snap action.

'L In combination, a main valve for controlling VtheA ilow of a iluid, apressure responsive motor for modulating the valve, pilot valve meansconsaid motor, a movable member for operating said pilot valve means, ailrst thermostat responsive to the temperature of the heated iiuid, asecond thermostat responsive to the temperature of the iiuid returnedfromsaid space, means connected to said two devices for exerting a.force on said member dependent upon the average of the values 4oi? saidtwo temperatures, follow up means exerting a force on said memberdependent upon the pressure on the outlet side of said main valvewhereby said member operates said main valve to modulate it inaccordance with the average of said two temperature values, and meansfor actuating said pilot valve means in a direction to cause closure ofsaid main valve, said last named pilot actuating means being operativeonly when the forces exerted by said thermostats and said.

follow up means decrease below a predetermined value.

l0. In combination, a main valve for controlling the flow of la fluid, apressure responsive motor ior modulating the valve, pilot valve meanscontrolling the pressure in said pressure motor, a movable member foractuating said pilot valve means, a condition responsive device exertinga force on said member depending upon the'value of said condition,follow up means responsive to the pressure on the outlet side of saidmain valve for balancing said force, and therefore modulating theposition of said main valve, and means opposing both said conditionresponsive device and said follow up means for actuating said pilotvalve means in a direction to kcause closure of said main valve, saidlast named pilot actuating means being operative only when the forcesexerted by said condition responsive device and said follow up meansdecrease below a predetermined value, said condition responsive devicebeing operative thereafter to actuate said pilot .valve means to opensaid lmain valve. said pilot actuating means preventing said follow upmeans becoming effective on said pilot valve means until after saidforces have increased to a predetermined value.

11. In combination, a main valve for controlling the flow of a iiuid, apressure responsive motor for modulating the valve, pilot valve meanscontrolling the pressure in said pressure motor,

, movable connecting means for actuating said pilot valve means, saidconnecting means comprising a pair of relatively movable members whichare biased apart, means responsive to a controlling condition acting onsaid connecting means with a force dependent upon the value of saidcondition, follow-up means responsive to the pressure on the outlet sideof said main valve exerting a balancing force on said connecting meansdependent upon the value of said pressure, said condition responsivemeans and follow-up means normally being eiective to hold said movablemembers together in apredetermined relation against their bias and toposition said connecting means in accordance with the relative value ofsaid forces, said members moving apart by reason of their bias wheneversaid two forces decrease below a predetermined value, and connectingmeans between one of said members and said pilot valve means effectiveto actuate said pilot valve means to close said main valve whenever saidmembers are apart.

lil. In combination, a main valve for controlling the flow of a iluid, apressure' responsive motor for modulating the valve, pilot valve meanscontrolling the pressure in said pressure motor.

movable connecting means for actuating said pilot valve means, saidconnecting meanscomprising a pair of relatively movable members. snapacting biasing means tending to move said members apart, meansresponsive to a controlling condition acting on said connecting meanswith a force dependent upon the value of said condition. follow-up meansresponsive to the pressure on the outlet side of said main valveexerting a balancing force on said connecting means dependent upon thevalue of said pressure, said condition responsive means and follow-upmeans normally being eil'ective to hold said movable members together ina predetermined relation against the action of said biasing means and toposition said connecting means in accordance with the relative value ofsaid forces, said biasing means being effective to move said membersapart with a snap action whenever said two connecting means between oneoi' said members motor for modulating the valve. pilot valve meanscontrolling the pressure in said pressure motor, movable connectingmeans for actuating said pilot valve means. said. connecting meanscomprising a pivoted lever, biasing means for rotating said lever to aposition where it actuates saidV pilot valve means to close said vave,means responsive to a controlling condition acting on s'aid connectingmeans with a force dependent upon the value of said condition, andfollow-up means responsive to the pressure on the outlet side of saidmain valve exerting a balancing force on said connecting means dependentupon the value of said pressure, said condition responsive means andfollow-up means normally being eil'ective vto render said biasing meansinoperative and to p0- sition said connecting means solely ln accordancewith the relative value oi' said forces, said biasing means beingeffective to rotate said lever to a position w'here it actuates saidpilot valve mans to close said valve whenever said two forces decreasebelow a predetermined value.

14. In combination, a main valve for controlling the flow of a fluid, apressure responsive motor for modulating the valve, pilot valve meanscontrolling the pressure in said pressure motor, movable connectingmeans for actuating said pilot means, said connecting means comprising arst pivoted lever and a second lever pivotally carried by said rstlever, means biasing said levers apart, means responsive to acontrolling condition acting on said connecting means with a -forcedependent upon the value of said condition, follow-up means responsiveto the pressure on the outlet side of said main valve exerting abalancing force on said connecting means dependent upon the value ofsaid pressure, said condition responsive means and follow-up meansnormally being effective to hold said levers to'- gether in apredetermined relation against their bias and to position saidconnecting means inaccordance with the relative value of said forces,said biasing means being effective to move said levers apart wheneversaid two forces decrease below a predetermined value, stop means tolimit movement of one of said levers, and connections between the otherof said levers and said pilot valve means effective to actuate saidpilot valve means toA close said main valve when said one lever is movedagainst said stop.

15. In combination, a main valve for controlling the iiow of a fluid, apressure responsive motor for modulating the valve, pilot valve meanscontrolling the pressure in said pressure motor,

movable connecting means i'or actuating said pilot valve means, saidconnecting means comprising a rst pivoted lever and a second lever piv-.o'tally carried by said rst lever, means biasing said levers apart,means responsive to a controlling condition acting on said connectingmeans with a force dependent upon the value oi' said condition,follow-up means responsive to the pressure on the outlet side of saidmain valve exerting a balancing force on said connecting means dependentupon the value of said pressure, said condition responsive means andfollow-up-means normally being eiective to hold said levers together ina predetermined relation against their bias and to position saidconnecting means in accordance with the relative value of said forces,said biasing means being eifective to move said levers apart wheneversaid two forces decrease below a. predetermined value, snap action meansassociated with said biasing means to cause said biasing means to movesaid levers with a snap action, stop means to limit movement of one ofsaid levers, and connections between the other of said levers and saidpilot valve means effective to actuate said pilot valve means to closeVsaid main valve when said one lever is moved against said stop.

16. In combination, a main valve for controlling the now-o a fluid, apressure responsive motor for modulating the valve, pilot valve meanscontrolling the pressure insaid pressure motor, movable connecting meansfor actuatng said pilot valve means, said connecting means comprising afirst pivoted lever and a second lever pivsure on the outlet side ofsaid main valve exerting a balancing force on said connecting meansdependent upon the value of said pressure, said condition responsivemeans and follow-up means normally being eifective to hold said leverstogether in a predetermined relation against their bias and to positionsaid connecting means in accordance with the relative value of saidforces, said biasing means being effective to move said levers apartwhenever said two forces decrease below a predetermined value, 'snapaction means associated with said biasing means, said snap action meanscomprising a toggle element disposed in a dead center positionwhen saidlevers are held in said predeterminedrelationand being effective whensaid levers start to move apart 'to cause them to move with a snapaction, stop means to limit movement of one of said levers, andconnections between the other of said levers and said pilot valve meanseffective to actuate said pilot valve means to close said main valvewhen said one lever is moved against said stop.

17. In combination, a valve movable between two extreme positionsforcontrolling `the flow of a iluid, means for positioning said valveincluding a movable connecting means and effective to cause said valveto assume a position intermediate said extreme position dependent uponthe position of said connecting means, said connecting means comprisinga. pair of relatively movable members, means biasing said relativelymovable members apart, means ,responsive to a controlling conditionacting on said connection means with a force' dependent upon thevalue ofsaid condition, follow-up means responsive to the pressure on the outletside of said valve exertiing a balancing force on said connecting meansdependent upon the value of said pressure, said condition responsivemeans and follow-up means normally being eiiective to hold said movablemembers together in a predetermined relation against said biasing meansand to position said connecting means in,l accordance with the relativevalue of said forces, and means including said biasing means moving saidmembers apart and thereby causing movement of said valve to an' extremeposition whenever said two forces de crease below a predetermined value.

18. In combination,a condition control device movable between twoextreme positions, movable connecting means connected vto said control ldevice for 'actuating the same, said connecting means comprising a pairof relatively movable members, means. biasing said relatively movablemembers apart, means responsive to a controlling condition acting onsaid connecting means with a force dependent upon the value of saidcondition, follow-up means responsive to a further condition directlyand substantially immediately effected' by said controly device, saidfollow-up means being effective to exert a balancing force on saidconnecting means dependent upon the value of said pressure, said firstnamed condition responsive means and follow-up means normally beingeffective to hold said movable members together in a predeterminedrelation against said biasing means and to position said connectingmeans and said control device intermediate said extreme position and inaccordance with the relative value' of said forces, said members beingmoved apart by said biasing means whenever said twoforces decrease belowa predetermined value, and means including said biasing meansfunctioning under lsuch conditions to cause said control device to moveto one extreme position.

DANIEL G. TAYLOR.

